Flare stacks are used quite extensively especially in the petroleum refining industry for the burning of combustible waste gases produced as a by-product of the refining process. This is necessary because the gases pose both a safety hazard from the standpoint of explosion and fire as well as a health hazard in the form of atmospheric pollution.
Although the flare stacks may be operated continuously, intermittent operation is more common because the waste gases are produced in varying quantities at different times thereby making it difficult to maintain a constant flow of gas through the flare stack. To assure that these intermittently produced waste gases will be ignited, it is commonplace to provide a continuously burning pilot in the vicinity of the discharge end of the flare stack. Although the pilot is intended to burn continuously, it will often be blown out by winds of high velocity which are quite prevalant at the elevation of the pilot. Furthermore, repairs and routine maintenance of the flare stack and igniting system will require that the pilot be extinguished and then subsequently reignited when normal operation is resumed. For this reason, means must be provided to rapidly and safely reignite the pilot in the event of this accidental or intended extinguishment.
The prior art is replete with various apparatus and methods for igniting the pilot burner, including the raising of a burning torch on a cable, firing a flare or tracer bullet in the vicinity of the pilot burner, and activating a sparking device which is mounted within the pilot burner itself. Another method is to provide a vertical ignition tube adjacent the pilot, flowing a combustible gas through the ignition tube and igniting same within the tube itself to produce a flame front which travels upwardly and out of the ignition tube to thereby ignite the pilot. In apparatus of this last mentioned type it is desirable to provide the pilot with a venturi or other adjustable air-gas mixing devices to assure that the mixture is proper for efficient and safe operation of the pilot over long periods of time. It is also necessary that the igniting tube be provided with an adjustable air-gas mixing device such a venturi or the like because the manner in which the flame front is initiated and propagated within the tube is highly dependent on the richness or leanness of the mixture as well as its rate of flow. Furthermore, in extremely cold climates, the ignition tube must be of sufficiently large diameter to assure that the flame front will not be extinguished before it has reached the discharge nozzle.